Are there advantages using a DD in Mono or Mono in DD. Whe chasing small gold.
DD in mono, Mono in DD on 4500
- Thread starter wick p
- Start date
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If you've got a commander "10 X 5 DD" in mono you'll get lots of small gold if it's there, however not much depth.
A DD in DD is good in trashy areas because you can use the discriminator to ignore ferrous rubbish.
A DD in DD is good in trashy areas because you can use the discriminator to ignore ferrous rubbish.
A DD coil will work in both DD or mono modes, but a mono coil will not work in DD mode.
A DD coil is essentially two separate D shaped coils side by side and overlapping in the centre by an inch or so along their straight sides.
When a mono signal is used it feeds to only one coil (the right coil from memory) and the left coil becomes inactive.
The effect is that the active shape then becomes a roughly semi-circular shaped mono coil eg for a round 11” DD coil the effective size becomes roughly a 11 x 6 lopsided D shaped mono coil.
Despite its unusual shape I used it very successfully on a GP extreme as back then larger mono coils did not handle difficult soils very well. The smaller 11 x 6 mono thus created was much less affected by the ground picked me up many small nuggets missed in the DD mode.
In terms of depth, I would be hard put to say whether the half size mono was losing me any depth over the full size DD, but I started to use the mono configuration as my default marking my transition from DD to mono searching.
It was only when the technology created in later machines made mono mode much stabler that larger mono coils became the normal search mode for most people.
An advantage even today would be that if you are unable to afford or the ability to carry a dedicated small elliptical mono coil then using a DD in mono would be an option. Also, if the ground noise conditions were found to be really patchy or working in trash areas having both DD and mono modes available at the flick of a switch could also be an advantage.
Remember though for pinpointing purposes that the left side of the round DD coil when running in mono will not be sensitive
A DD coil is essentially two separate D shaped coils side by side and overlapping in the centre by an inch or so along their straight sides.
When a mono signal is used it feeds to only one coil (the right coil from memory) and the left coil becomes inactive.
The effect is that the active shape then becomes a roughly semi-circular shaped mono coil eg for a round 11” DD coil the effective size becomes roughly a 11 x 6 lopsided D shaped mono coil.
Despite its unusual shape I used it very successfully on a GP extreme as back then larger mono coils did not handle difficult soils very well. The smaller 11 x 6 mono thus created was much less affected by the ground picked me up many small nuggets missed in the DD mode.
In terms of depth, I would be hard put to say whether the half size mono was losing me any depth over the full size DD, but I started to use the mono configuration as my default marking my transition from DD to mono searching.
It was only when the technology created in later machines made mono mode much stabler that larger mono coils became the normal search mode for most people.
An advantage even today would be that if you are unable to afford or the ability to carry a dedicated small elliptical mono coil then using a DD in mono would be an option. Also, if the ground noise conditions were found to be really patchy or working in trash areas having both DD and mono modes available at the flick of a switch could also be an advantage.
Remember though for pinpointing purposes that the left side of the round DD coil when running in mono will not be sensitive
A mono coil will work in DD switch position no problem. Remember, this switch used to be called the Rx switch and was labelled Normal, and E (enhance) when it first appeared on the GP extreme. The reason for this was because regardless of switch position the Tx was always the same, the left side Transmit winding always did the transmitting. All that changed was what happened on the Receiving side of things.
So with a DD coil:
In Normal/DD
Left winding - Transmits
Right winding - Receives
In Enhance/Mono
Left winding - Transmits
BOTH SIDES - Receive
In Cancel
Left Winding - Transmits
Both sides - Receive, but one side is +(positive) and the other is -(negative)
So, in my view, a DD is only using half the coils diameter, whereas when in Mono mode, its using half the coil for transmitting, and the whole coil for receiving.
Geoff is correct in that on an 11" DD coil, running it in the Mono mode effectively creates an 11x6" mono, but it's actually the Left side of the coil that is most sensitive. Performance wise, it's like a blend of 11" DD and 8" Mono. Not quite as sensitive as an 8" mono, but handles bad ground a lot better.
So this E/Mono position was initially designed with DD coils in mind, but was soon found to also work with Mono coils. Whatever maths/electronic switching was going on to allow the Rx switching to work also had the effect of a slightly smoother threshold when using a straight mono coil. But, I think there is a very slight drop in audio as well, but seems to vary a bit with different coils.
I have found that certain mono coils are a little "brighter" when run in DD, with negligible difference in threshold stability, whereas others are clearly more settled in the Mono position. So definitely pays you to do some testing with your Mono coils and see which positions responds better. Testing on some buried targets before disturbing the ground is the best way, and you will see when you switch from DD to Mono you will usually have to re ground balance.
Results may also vary with different timings.
So with a DD coil:
In Normal/DD
Left winding - Transmits
Right winding - Receives
In Enhance/Mono
Left winding - Transmits
BOTH SIDES - Receive
In Cancel
Left Winding - Transmits
Both sides - Receive, but one side is +(positive) and the other is -(negative)
So, in my view, a DD is only using half the coils diameter, whereas when in Mono mode, its using half the coil for transmitting, and the whole coil for receiving.
Geoff is correct in that on an 11" DD coil, running it in the Mono mode effectively creates an 11x6" mono, but it's actually the Left side of the coil that is most sensitive. Performance wise, it's like a blend of 11" DD and 8" Mono. Not quite as sensitive as an 8" mono, but handles bad ground a lot better.
So this E/Mono position was initially designed with DD coils in mind, but was soon found to also work with Mono coils. Whatever maths/electronic switching was going on to allow the Rx switching to work also had the effect of a slightly smoother threshold when using a straight mono coil. But, I think there is a very slight drop in audio as well, but seems to vary a bit with different coils.
I have found that certain mono coils are a little "brighter" when run in DD, with negligible difference in threshold stability, whereas others are clearly more settled in the Mono position. So definitely pays you to do some testing with your Mono coils and see which positions responds better. Testing on some buried targets before disturbing the ground is the best way, and you will see when you switch from DD to Mono you will usually have to re ground balance.
Results may also vary with different timings.
